1. Field of the Invention
The present invention relates to a recording medium formed of paper, various types of resin film, metal, etc. on which information is recorded as optically readable dot codes and a reading apparatus for reading the dot codes recorded on the recording medium. More specifically, the present invention relates to a reading apparatus capable of eliminating an adverse effect of a flaw or dust on the recording medium upon reading a pattern of the dot codes.
2. Description of the Related Art
Various recording mediums such as magnetic tapes and optical disks for recording voice information, music information, and the like have been known conventionally. The unit price of these mediums is somewhat high even though their reproductions are mass-produced, and a very large space is required for keeping them. Furthermore, it takes time and trouble to transfer a recording medium on which voice information is recorded from one person to another person far away therefrom, even though it is mailed or sent by hand.
The above problems are true of so-called multimedia information including video information acquired from cameras, video equipment, etc., digital code data (text data) obtained from personal computers, wordprocessors, etc., and the like.
A system for recording/reproducing multimedia information on/from a sheet of paper, various types of film, metal, etc. in the form of image information, i.e., dot code which can be sent by facsimiled and mass-reproduced at low cost, was invented and filed as International Application No. PCT/JP93/01377. This application was published on Apr. 14, 1994 as International Publication No. WO 94/08314.
The dot code is formed of a plurality of two-dimensionally arranged blocks, as illustrated in FIG. 16 of the international application. Each of the blocks includes a marker, data of x and y addresses of the block, data for detecting and correcting an error of the addresses, and a data area in which data is actually stored. The dot of the marker and that of the data are different in size such that they can be distinguished from each other. The recording/reproducing system therefore has a dot code structure wherein the location of data can be specified by detecting that of the marker.
A reading apparatus for reading the multimedia information is constituted as shown in FIG. 17 of the above international application. The dot code recorded on a recording medium is scanned and the image is picked up by an image pickup device. An image signal corresponding to the image is decoded to reproduce the original multimedia information. The reading apparatus is so constituted that the multimedia information can be correctly reproduced even if the dot code is scanned obliquely.
However, if dot code is printed on a recording medium of ordinary paper with commonly-used ink or toner and the reading apparatus is brought into contact with the recording medium, or friction occurs between them, the pattern of the printed dot code may disappear or the ink may blur on the paper. Consequently, the original multimedia information cannot be reproduced correctly.
Moreover, if a flaw or dust is attached to the surface of the pattern, it is projected on the image pickup device and formed as an image. Thus, the pattern is read incorrectly, and the original multimedia information cannot be reproduced correctly.